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Vol 4: Impact of heterocirculene molecular symmetry upon two-dimensional crystallization.This article is from Scientific Reports, volume 4.AbstractDespite the development of crystal engineering, it remains a great challenge to predict the crystal structure even for the simplest molecules, and a clear link between molecular and crystal symmetry is missing in general. Here we demonstrate that the two-dimensional 2D crystallization of heterocirculenes on a Au111 surface is greatly affected by the molecular symmetry. By means of ultrahigh vacuum scanning tunneling microscopy, we observe a variety of 2D crystalline structures in the coverage range from submonolayer to monolayer for D8h-symmetric sulflower C16S8, whereas D4h-symmetric selenosulflower C16S4Se4 forms square and rectangular lattices at submonolayer and monolayer coverages, respectively. No long-range ordered structure is observed for C1h-symmetric selenosulflower C16S5Se3 self-assembling at submonolayer coverage. Such different self-assembly behaviors for the heterocirculenes with reduced molecular symmetries derive from the tendency toward close packing and the molecular symmetry retention in 2D crystallization due to van der Waals interactions.